This invention relates in general to a non-linear non-circular coiled spring, and in particular to a non-linear non-circular coiled spring having twisted transition portions for providing a non-linear property.
FIG. 5 is a side view showing a conventional typical non-linear coiled spring. In FIG. 5, a non-linear coiled spring 10 is circular in spring cross-section, and obtains a non-linear property, in which the spring constant changes with the value of load. In other words, the load-deflection property is not linear, that is, non-linear by varying its pitch in an "A" region and a "B" region in an axial direction, or by making an unequal-pitch spring.
FIG. 6 is a graph showing the load-deflection property or spring constant of the above-mentioned non-linear coiled spring. In FIG. 6, the resultant value of the spring in the A region and the B region is K.sub.1, and the value of the spring constant in the B region is K.sub.2. The value of the varied ratio K.sub.2 /K.sub.1 of the spring constant is approximately 1.4. Therefore, it is difficult to obtain a larger varied ratio due to the fact that a pitch in one region must be made far larger than in the other region in manufacturing, etc.
In the meantime, there is a non-circular coiled spring of rectangular, including square, cross-section, different from the coiled spring of circular cross-section. FIG. 7 is a side view, including a sectional view, showing a conventional non-circular coiled spring. In FIG. 7, the non-circular coiled spring 20 is rectangular in cross-section, in which its longitudinal length is "b", and its lateral length or width is "a". When it is completely compressed, the upper surface portions and lower surface portions of the spring are, respectively, engaged with each other, and therefore this spring provides more stability than the coiled spring of circular in cross-section, which result in less occurrence of damage. Moreover, this spring can obtain a larger deflection, and can vary the spring constant by change of pitch as well as change of ratio of longitudinal length to lateral length.
In general, when the usage of the coiled spring is considered, it is applicable as a mechanical spring or as a car suspension spring. Since the non-linear non-circular coiled spring in accordance with the present invention is particularly adapted to be used as a car suspension spring and a mechanical spring, the explanation will be made with regard to a conventional suspension spring and a conventional mechanical spring.
FIG. 8 is a side view showing a prototype of a car suspension. In FIG. 8, the suspension comprises a suspension spring 30, washers 32 and 34 attached to the spring 30 at its opposite ends, an attachment member 35, a shaft 36 extending from the attachment member 35 through the spring 30, and a nut 38 attached to the shaft 36 at its thread portion.
In use, the suspension is used in a condition that the attachment member 35 is disposed downward. The attachment member 35 is attached to the frame, not shown, of the wheel side, the frame of the car body is positioned on washer 34, and is prevented by the nut 38 from separating from the suspension. This suspension is used as a suspension itself as well as a damper.
However, when it is used as a damper, it is preferred that the damper supports the weight of the car body to be deflected largely. On the other hand, when it is used as a suspension, it is preferred that the deflection in the suspension is smaller to absorb more effectively the vibration generated when the car running. The conventional suspension spring of this type could not satisfy both spring properties, that is, large deflection property and small deflection property.
An improved car suspension was proposed in order to eliminate the above-mentioned disadvantages. FIG. 9 is a side view showing the conventional improved car suspension. In FIG. 9, in the suspension, another washer 32' is added between the washer 32 and 34 of the suspension shown in FIG. 8 and another auxiliary spring, a so-called helper spring 30' is added between the washer 32 and 32'. The coiled spring of circular in cross-section is used as a main spring 30 and the non-circular coiled spring which can have a large value of deflection is used as a helper spring 30'. The helper spring 30' is designed to have a value of deflection so that the spring should be completely compressed by the weight of the car, and its upper surface portions and lower surface portions are engaged with each other, which results in no clearance or gap. Consequently, only main spring 30 functions as a suspension.
FIG. 10 is a side view showing a conventional mechanical spring. In FIG. 10, with the mechanical spring, two springs which have different spring constants, that is, a main spring 40 for high load and a sub-spring 40' for low load, are disposed on the upper and lower sides of the washer 42. The arrangement of the springs is used in a machine such as a press. In addition to the spring 40, the spring 40' is disposed in series with the spring 40 in order to preclude play by the strokes made in the machine.
As mentioned above, although the non-circular coiled spring is used in accordance with the usage in place of the coiled spring of circular in cross-section, there has been no non-circular coiled spring which has a non-linear property. In order to provide a non-circular coiled spring with a non-linear property it is in general considered that the pitch is varied in a similar manner to the coiled spring of circular in cross-section as shown in FIG. 5. In such a case, it is difficult to set a large varied ratio of spring constant.
In the meanwhile, in the improved car suspension, two different types of coiled springs are used, and in addition more washers are required, and therefore a larger number of necessary members is required.
Furthermore, for the machine spring, two springs of different spring constants, and the washer therebetween are used, and therefore there is also a disadvantage that a larger number of necessary members is required.